Ignition Control

Ignition control is one of the more involved parts of the DIYPNP installation to set up, and may take a bit of trial and error if you do not have an application guide to cover what mods you need. This page will explain the ignition control, both the inputs and the outputs. We’ve made the DIYPNP flexible enough to cover many different types of possible ignition systems.

Ignition Inputs

The MicroSquirt Module has three ignition input circuits, two which can be used for various types of crankshaft position sensors and a third for camshaft position sensors (aka second trigger or G sensors). Here’s how to tell which circuit you need.

Some ECUs only control the fuel and get their RPM signal off the negative terminal of the coil. If you have one of these, connect the ECU pin that goes to the coil negative to OPTO IN + and connect OPTO IN – to a 12 volt pin through a 4.7K resistor. A version of this uses a 12 volt square wave instead of the coil negative; if you have this, connect OPTO IN + to the signal connection and put a jumper across the two pins of Opto GND.

For an optical or Hall effect crankshaft position sensor, most of the time you’ll wire OPTO IN + to the sensor and put a jumper across the two pins of OPTO GND. Many of these need a pull up resistor; in most cases, a 1K resistor in the 12 volt position on R3 will do the trick. There are a couple of other circuits you can try if this doesn’t give a steady signal. The most common versions are to use different pull up resistors, or to remove the Opto GND jumper, do not connect OPTO IN +, and connect OPTO IN – to the sensor. If connecting Opto IN – to the sensor, you must have a pull up resistor – the circuit won’t work without it. This version requires the opposite Ignition Input Capture setting from the normal version.

Variable reluctor sensors, sometimes called VR sensors, inductive pickups, or magnetic pickups, have two wires, and possibly a third shield wire. Connect the positive wire to VR+ and the negative wire to VR-. Sometimes it may take a bit of trial and error to find out which is which since factory wiring diagrams often do not mark these clearly. If you have a shield wire, connect it to GND. Tip: If your sensor is connected to a wheel with a large number of teeth, like a Ford 36-1 or a Bosch 60-2, and you’re losing the tach signal at high RPM, put a 10K resistor in line with the wire going to VR+. This will usually clear things right up.

The camshaft position sensor input is marked VR2. It’s actually a kind of hybrid circuit that works with Hall effect, VR, and optical sensors. Hall or optical sensors may need a pull up, just like with the crankshaft position input. VR sensors with a separate ground wire should have this wire connected to SG. The VR2 circuit has a built in threshold that some VR sensors may not trigger correctly at low RPM. If this happens on your car, take a 51K resistor and run it from the ALTCAM connection to ground. This will lower the threshold voltage. Many Nippondenso ignitions will need this mod.

Ignition outputs

Depending on your ignition module, there are several possible circuits you can use. Here’s a guide to the various options.

Basic Logic Level Output

Rule of thumb: This is the most common spark output configuration on Mazda, Mitsubishi, and Toyota vehicles. If you have one of these cars, try starting with this setup.

On cars that use this, the ignition module is controlled by a voltage signal from the ECU. Usually, it starts charging the coil when it gets a 5 volt signal from the ECU, and fires the coil when the signal goes back to 0 volts. This is a fairly simple setup. Just start with the four pin header near Input 1, and jumper these outputs to your ignition module connections on the adapter board.

Spark A: IGN1

Spark B: IGN2

Spark C: WLED (requires MS2/Extra 2.1.1 or higher)

Spark D: ALED (requires MS2/Extra 2.1.1 or higher)

Spark outputs C and D also need pull ups. A typical pull up setup is to put a 100 ohm resistor in the 5 volt position for both R1 (spark D) and R2 (spark C).

Virtually all setups that use this mod will have the spark output set to Going High / Inverted. Check to be sure the ignition module doesn’t get hot when you have the key on and the engine off; if it does, reverse the spark output setting.

Direct Coil Control

Rule of thumb: If your coil has only two terminals, and there’s no ignition module outside the ECU, use this. Also applies to 4 cylinder coil packs with 3 terminals and 6 cylinder coil packs with 4 terminals when not used with an external ignition module.

Common in Bosch and Seimens ECUs, almost unheard of in ECUs of Japanese origin. There is no external ignition module, and the ECU controls the current running through the coil directly with a power transistor. We’ve put four Bosch BIP373 power transistors in the DIYPNP for these types of ignitions. On cars which originally used an external ignition module, this can open up other ignition options directly controlled by the ECU. For example, if you want to convert your ’90-’97 Miata to use one MSD coil for each plug, you can use these outputs to fire the coils without an external ignitor.

For normal operation (each spark output driving one coil), install the Enable jumpers next to each of the four high current ignition outputs. For wasted spark COP on a four cylinder engine (firing four coils from two spark outputs), install the Enable jumpers on spark outputs 1 and 2. Then take a length of jumper wire and connect the round hole on the Spark 3 Enable jumper and run it to either end of the Spark 1 Enable jumper. Connect the round hole of the Spark 4 Enable jumper to the Spark 2 Enable jumper.

If using spark outputs C or D, you’ll need to install 100 ohm, 5 volt pull up resistors in the R2 and R1 slots respectively.

Ground Triggered Logic Level

Rule of thumb: If it’s a Honda and has a distributor, use this.

A much rarer sort of ignition module, but examples that do this include the Bosch 139, most Hondas, and the MSD 6AL also falls into this category if you have its white wire connected directly to the DIYPNP (If you have it connected to a stock ignition module, base your mods on what the stock ignition module would need). A ground triggered ignition module doesn’t run the coil current through the ECU, but instead it pulls a signal on the factory ignition module to ground. For Honda ignition modules, connect IGN1 to the In terminal on Relay 1, and connect the Out terminal of Relay 1 to the ignition module pin on the adapter board.